Surveillance cameras installed on ceilings and walls of facilities and buildings that use a varifocal lens have been known. A varifocal lens is a simplified version of a zoom lens and involves focus adjustment when zooming is performed. Focus adjustment of the varifocal lens can be accomplished by manually rotating a focus ring provided on a lens barrel. Such a mechanism is disclosed in Japanese Patent Laid-Open No. 5-323422 (pp. 3-4, FIG. 1), for example.
For a surveillance camera that uses such a varifocal lens, a monitor that outputs camera images are often provided in a location (for example in a surveillance monitor room) remote from the location where the surveillance camera is installed. In such a case, installation of the surveillance camera is performed usually by two operators. For example, one of the operators operates the camera to adjust the focus at the surveillance camera installation location and the other watches the monitor to check whether the focus is correct or not.
However, in conventional focus adjustment methods, it is not easy to achieve accurate focus and it takes a lot of labor and trouble for the installation since two operators perform focus adjustment in cooperation.
To save the labor and trouble required for the installation work, one operator performs focus adjustment without the help of others when installing the surveillance camera. Specifically, an operator who is installing the surveillance camera adjusts focus while watching a small portable monitor to check whether the focus is correct or not. However, although the operator may have confirmed on the small portable monitor that the correct focus has been achieved, the operator sometimes finds that an image on a large-screen monitor installed in a location such as a surveillance monitor room is defocused.